Reversible Diels-Alder based polymers are generally known, and have been investigated for use in solid ink printing. These are disclosed, for example, in U.S. Pat. Nos. 5,844,020, 5,952,402, and 6,042,227. These reversible Diels-Alder based polymers would be particularly useful in ink jet applications, because the ink jet apparatus allows for precise, imagewise control of the placement of material, and thus would allow for the production of precise, hard polymer films possessing the reversible solid-to-liquid conversion properties.
However, the Diels-Alder based polymers previously investigated suffered from long solidification times after being deposited on a substrate. For example, it was found that many of the prior Diels-Alder based polymers had solidification times on the order of several hours, making them unsuitable for use in most printing applications. Long solidification times are unsuitable because while the printed material remains in a liquid or semi-liquid state, the image can become distorted, image quality can degrade, and the printed images cannot be stacked on top of each other resulting in either large space needs or low throughput.
Another difficulty with some Diels-Alder based polymers is that it has been found that prolonged heating of the molten liquid of some reversible polymer mixtures can lead to a 2+2 cycloaddition reaction. As a result of the cycloaddition reaction, an irreversible polymerization or hardening of the material can occur, which can shorten the useful working lifetime of the composition and can render the composition unacceptable for some uses such as in a solid inkjet printer.
Accordingly, there is a need for improved materials that exhibit the reversible polymerization property, but that have shorter solidification times and/or are more stable against premature irreversible polymerization, to permit their efficient and economical use in commercial processing, such as in conventional ink jet printing. There is also a need for a hard polymer material that can be formed from a liquid having very low melt viscosity, such that it may be suitable for jetting at typical ink jet operating temperatures and in a precise imagewise fashion, but that can retain its desired properties despite repeated heating and cooling of the composition and/or despite long-term heating of the composition.